(a) Field of the Invention
The present invention relates to a method for receiving signals in a mobile communication network, and a base station thereof. More specifically, the present invention relates to a method for reducing complexity of a base station when the base station uses two two-branch polarization antennas to receive signals through four branches.
(b) Description of the Related Art
In general, signals transmitted from a mobile station antenna are reflected or refracted depending on environmental factors such as the ground or buildings, and they are received to a base station antenna through multiple paths. As described, when various signals are received through different paths, the signals undergo different amplitude attenuations and phase changes. When the signals are combined, signal intensities change according to time variation differing from the signal intensities of transmission signals, which is referred to as fading. To solve the problem of fading, diversity methods for receiving various independently-faded signals and appropriately combining them have been proposed.
The diversity methods include a space diversity method which is a method of transmission by the simultaneous use of two or more physically separated vertical antennas, and a polarization diversity method for separately receiving vertical polarization and horizontal polarization signals. The polarization diversity method uses a polarized antenna to detect polarized signal components and uses them as branches of diversity.
Base stations based on the mobile communication systems such as IS-95, CDMA2000, and WCDMA generally use the space diversity method by using two vertical antennas spatially separated for each sector to receive signals. In this instance, the reason for using less than three antennas is that less merits are achieved compared to an increase of complexity. The above-noted mobile communication systems usually adopt the three-sector method of using three sectors α, β, and γ. Referring to FIG. 5, a conventional configuration of a base station and a method for receiving signals at the base station will be described.
FIG. 5 shows a conventional base station.
As shown, the conventional base station (e.g., a base station using the three-sector method) includes RF/IF (radio frequency/intermediate frequency) processors RF/IF1 through RF/IF6 for each antenna path. The signals received through the six vertical antennas are passed through the RF/IF processors to be converted into baseband signals, and are input to a modem processor 20.
The modem processor 20 searches multipath signals for the six antenna reception paths to allocate a valid multipath signal component to a finger, and detects a phase of the corresponding multipath signal component to execute MRC (maximal ratio combining) on the signal components allocated to the finger.
In detail, the two antennas in each sector are spatially separated to receive signals with independent fading and phase, but they are not so far from each other that spreading sequence offsets of the signals received at the two antennas differ. Therefore, the signals that have the same spreading sequence offset and different phase and fading are received through the two antennas, and the modem processor 20 performs phase detection and phase correction on these signals, and executes MRC to obtain a diversity effect. So as to achieve the diversity effect, it is required for the respective antenna components to maintain independent signal paths without being added until MRC is executed on them after the phase detection and phase correction.
Recently, a method using two sets of two branch X-pole antennas for enabling usage of both space diversity and polarization diversity has been proposed. That is, when two sets of X-pole polarized antennas are provided for each sector, the polarization diversity characteristics can be obtained through the X-pole antennas, and since the two sets of X-pole antennas are spatially separated, space diversity characteristics can be obtained.
As shown in FIG. 6, in the two sets of two-branch X-pole antennas 41 and 42, 43 and 44, and 45 and 46, each sector has four branches 41a, 41b, 42a, and 42b; 43a, 43b, 44a, and 44b; and 45a, 45b, 46a, and 46b. Accordingly, twelve RF/IF processors RF/IF1 through RF/IF12 coupled to each branch are to be formed in the base station (e.g., a three-sector base station), and a modem processor 50 having twelve receivers for receiving signals from the twelve RF/IF processors is to be used.
Hence, the number of the RF/IF processors and signal paths increase to increase hardware complexity, and the conventional modem processor is to be modified.